What features tell you the sex of the bird?
When they are old enough, the comb on a male gets very large. Prior to that, the shape of the crest should give you clues. A male's crest has "streamers" which are longer feathers that stick out at odd angles. A female's crest should look more like a Pom Pom. In the pics of the one I posted above, I thought I had a young cockerel until she was about 4 months old. Silkies are notoriously difficult to sex :/